Polarization is a useful probe to investigate the geometries and dynamics of outflows in BAL QSOs. We perform a Monte Carlo simulation to calculate the polarization produced by resonant and electron scattering in BALR. We find: 1) A rotated and funnel-shaped outflow is preferred to explain many observed polarization features. 2) Resonant scattering can contribute a significant part of the N V emission line in some QSOs.